The proposed research would focus on the development of improved methods for the diagnosis of Brucella canis (B. canis) and seek means for prevention of the disease. Canine brucellosis, virtually unknown a few years ago, has emerged as an important disease affecting the reproductive performance of breeding colonies of dogs. Standardized methods for diagnostic or seroepidemiological investigations would be developed. One portion of the investigation would thoroughly analyze and evaluate a variety of serological methods with the aim of providing an experimental basis for judging their relative sensitivities and specificities. Since B. canis is naturally mucoid, standard technics developed for smooth brucella cannot be exploited directly. We would systematically study the humoral antibody responses of specific pathogen free(SPF) dogs from the time of infection until a period at least 3 months after the bacteremia had ceased, using the several methods now employed on an empiric basis. Serological studies would be done in concert with bacteriological evaluations. A novel immunodiffusion test utilizing an antigen extracted from the outer cell wall of B. canis would be critically appraised and compared with other methods. Attempts would be made to isolate a type-specific antigen of improved specificity. Antigen specificity would be evaluated by tests with mono-specific B. canis antisera prepared in SPF dogs, a panel of heterospecific serums raised against antigenically related organisms, and a library of sera obtained in the field that react nonspecifically with B. canis. Tests would be evaluated by field study of a population of dogs known to have an exceptionally high prevalence of brucellosis. A second line of research would focus on the protective immune response to B. canis. A variant strain (M-) derived by selection from wild type B. canis has characteristics that suggest it may prove useful as a vaccine strain.